The pressure from sitting in a single position for an extended period of time cuts off circulation to vulnerable parts of the body. As a result, patients who are bound to a wheelchair for extended periods of time may develop pressure sores or pressure ulcers. Tilt-in-space wheelchairs have been developed to transfer pressure from the seat surface to the back surface by tilting or reclining a seated patient. While conventional tilt-in-space wheelchairs are effective at shifting weight and pressure for patients who cannot otherwise do so, they are deficient in other ways. For example, some tilt-in-space wheelchairs may cause sudden shifts in the center of gravity of a seated patient. A sudden shift in the center of gravity of a patient may produce a falling sensation and a startle reflex as a result. Startle reflex may cause hypertonia in some patients, which is characterized by increased tightness of muscle tone that may lead to loss of function and deformity.
U.S. Pat. No. 7,007,965 is directed to a tilt-in-space wheelchair having a seat supported relative to a base by a rocker that has a constant curvature and is designed to maintain the center of gravity of a wheelchair occupant at a fixed location during tilting. In order for the center of gravity of the wheelchair occupant to remain at a fixed location during tilting, however, the focal point of the curve of the rocker must coincide with the center of gravity of the wheelchair occupant. Because different wheelchair occupants may have different centers of gravity that may not be easily determined, the wheelchair may need significant adjustments to ensure that the focal point of the curve of the rocker coincides with the center of gravity of the wheelchair occupant.